ABSTRACT ? Overall Significant progress in basic immunology research over the last three decades has resulted in numerous medical advances and dissected the general mechanisms by which the human immune system responds to foreign antigens. However, a much more substantial understanding of the coordinated molecular mechanisms involved in eliciting immunity will be required, as each viral pathogen poses unique challenges to the immune system and the elicited immune responses are characterized by substantial heterogeneity that impacts disease susceptibility and pathogenesis. Indeed, it is expected that B-cell responses against diverse viral pathogens are uniquely evolved during infection to shape the functional activity of IgG antibodies. Studies from viral infectious diseases have shown that antiviral IgG antibodies have the capacity to mediate a wide spectrum of opposing functions: (i) protective functions, including neutralization, viral opsonization, and clearance of infected cells and (ii) pathogenic activities, which enhance viral infectivity, disease susceptibility and severity; a phenomenon termed as antibody-mediated enhancement (ADE) of disease. ADE mechanisms have been previously suggested to account for susceptibility to dengue disease, as epidemiological data support that prior flavivirus infection is the major risk factor for dengue disease, implicating the presence of cross-reactive, non-neutralizing IgG antibodies to this process. Understanding the heterogeneity of IgG responses elicited upon infection or vaccination with diverse viral antigens is therefore critical for characterizing the immunological mechanisms that drive human immunity and determine the protective vs. pathogenic activity of IgG antibodies. Our Center will feature three Projects directed by Drs. Ravetch (Project 1: Fc domain effector activity in dengue disease), Nussenzweig and Rice (Project 2: Understanding B cell memory in response to diverse virus infections), and Wang (Project 3: Immunity to dengue viruses), supported by a scientific core (Core A: Transgenic mouse core) and the administrative core (Core B). Through a series of collaborative studies between the three Projects, our Center aims to study human antiviral immune responses during infection and vaccination and characterize the immune mechanisms that regulate the function of IgG antibodies in humans. More specifically, we aim to characterize the heterogeneity of IgG responses elicited upon vaccination or infection with diverse viral pathogens, including HBV and flaviviruses, like Zika and dengue. Additionally, we will dissect the ADE mechanisms by which IgG antibodies mediate disease-enhancing activities and contribute to dengue disease susceptibility and pathogenesis. These studies will provide novel insights into the mechanisms that drive protective immunity and modulate antibody function, having a broader impact on the development of vaccination strategies against infectious pathogens.